Hi,

In order to calculate HOMO & LUMO, one needs .chk file and convert it to .fch file.

If you want to convert .chk into .fchk, kindly use the line:

formchkfile.chk (press enter)

1. wavefunction

2. gaussview

Dear Shilendra,

The chk file is used to rerun an optimization of a molecule. Sometimes for some reason the calculations are stopped or terminated. Instead of running the geometry from the beginning (initial geometry) you use the chk file that contains the last optimized structure. Therefore, by using the chk file you save many hours of calculations.

Software to be used as indicated by Oleg,

formchk converts the data in a Gaussian checkpoint file into a formatted form which is suitable for input into a variety of visualization software.

http://www.gaussian.com/g_tech/g_ur/u_formchk.htm

http://www.ccl.net/cca/documents/dyoung/topics-orig/checkpoint.html

Hoping this will be helpful,

Rafik

Thank You Dear Dr. Rafik Karaman and Dr. Oleg Gromov for your kind help and support always on researchgate. It is very useful for me. Earlier in case of error terminated output, I took standard geometry from log file then I used to paste in input file after that I submitted the job.

Now with chk file as you told without copy paste in input file from log file I can run the job. I  think some tag will be there for reading the chk file. I will go through the manual.

Thank You

Shilendra

As suggested above you can use .chk to rerun jobs from the checkpoint in an automatic way (not by visualizing and saving the last geometry from the output file). To do that your original, first input should have the following line (usually the 1st/2nd line):

%chk=file.chk

If you have that and the jobs fails for whatever reason, you can rerun the job by providing the following lines:

%chk=file.chk

# STANDARD GAUSSIAN INPUT LINE(S)

# geom=checkpoing guess=read

title

charge multiplicity

And that's it - you don't have to specify the geometry, as it will be read from the gaussian chk file. 

Bear in mind, however, that if you're using GEN (or GENECP) option you still have to provide the basis sets, as these are normally not read from the .chk file. If you want to also use the basis sets from the chk file you have to additionally specify "chkbasis" in place where you normally put your basis set (so e.g. B3LYP/chkbasis instead of B3LYP/6-31G* or B3LYP/gen).

But chk files have much more information in them (that's why they're so big), including usually all orbitals, wave-functions and so on, which can be changed to other formats and/or visualized by gaussview and other software.

Thank You Dear Dr. Bartosz Trzaskowski for your help.

I want to ask you other than GassView which software is suitable for reading chk file. Avagadro reads fchk file but I do not know how does convert chk file into fchk file.

In my system GaussView is not reading chk file. Might be some utilities is not available in my GaussView. When I choose option to read chk file it shows some error.

Shilendra

http://www.gaussian.com/g_tech/g_ur/u_formchk.htm

Hi,

In order to calculate HOMO & LUMO, one needs .chk file and convert it to .fch file.

If you want to convert .chk into .fchk, kindly use the line:

formchkfile.chk (press enter)

Hi,

As stated above you can use check point file to restart any calculation that has been terminated abruptly and addition to that you can use check point file as an initial starting point for any further calculations for instance going from geometry optimization to excited state calculations.

Now, converting check point file to formatted check point file is easy, in terminal(linux) type this:

formchk myfile.chk myfile.fchk

and its done.

Hope This Helps

Regards

Ajay Khanna

To convert .chk to .fch file.... https://www.youtube.com/watch?v=HZkAfPpDX-s